Heretofore, the present applicant and related corporations associated therewith have been provided various-types of actuators provided with dust-proof mechanisms or like such as disclosed in the following Patent Document 1 (which include motion guide devices for guiding motions of objects to be moved. For example, a leaner actuator provided with a dust-proof mechanism provided in the Patent Document 1 is provided with a function to surely prevent dust or like from leaking through an opening formed in an actuator housing, and in order to avoid interference between a dust-proof belt and a projected portion of a moving stage at the opening of the actuator housing, by-pass or detour means of the dust-proof belt with respect to the moving stage is specifically provided.
The linear actuator provided with the dust-proof mechanism disclosed in the Patent Document 1 will be explained hereunder with reference to FIG. 10. It is further to be noted that FIG. 10 is a view for explaining structure of a linear actuator provided with a dust-proof mechanism according to a conventional technology, in which (a) illustrates an upper surface side of the linear actuator provided with the dust-proof mechanism, (b) illustrates a front surface side thereof, and (c) illustrates a sectional view of the linear actuator provided with the dust-proof mechanism.
As shown in FIG. 10, the linear actuator 1 provided with a dust-proof mechanism according to the conventional art includes a slender (long and thin) box-shaped housing member 2, a ball screw 3 supported within the box-shaped housing member 2 in a state of being rotatable, a movable stage capable of reciprocally linearly moving in response to the rotational motion of the ball screw 3, and a drive motor 5 for driving and rotating the ball screw 3.
The housing member 2 is provided with a horizontal substrate 21, a pair of lateral vertical side plates 22 and 23 vertically standing from the horizontal substrate 21 and extending in parallel with the ball screw 3, and end blocks 24 and 25 mounted to front and rear end portions of the vertical side plates 22 and 23, respectively. One end of the ball screw 3 is supported by one of the end blocks 24 to be rotatable, and the other end of the ball screw 3 is also supported by the other one of the end blocks 25 to be rotatable in a manner of penetrating the end block 25 and being coupled with a drive motor 5 side.
The lateral vertical side plates 22 and 23 have upper end portions which are bent toward inside at right angle as horizontal upper plate portions 22a and 23a. A central partitioning (sectioning) plate 26 is disposed at an intermediate portion between the lateral horizontal upper plate portions 22a and 23a, and front and rear end portions of the central partitioning plate 26 are mounted and fixed to the end blocks 24 and 25, respectively. As a result of such arrangement, a left side opening 27 is formed between the horizontal upper plate portion 22a and the central partitioning plate 26 so as to extend in an axial direction of the ball screw 3, i.e., moving direction of the movable state 4. Likely, a right side opening 28 is formed between the horizontal upper plate 23a and the central partitioning plate 26.
The respective openings 27 and 28 are closed and sealed off by dust-proof belts 29 and 30 each having a width larger than a width of each opening. The dust-proof belts 29 and 30 are stretched between the end blocks 24 and 25 along the loser surface sides of the horizontal upper plate portions 22, 23 and the central partitioning plate 26.
As described above, the housing member 2 constitutes a compartment sectioned in shape of box by the horizontal substrate 21, the vertical side plates 22, 23 (i.e., horizontal upper plate portions 22a, 23a), the central partitioning plate 26, the end blocks 24, 25, and the dust-proof belts 29, 30 closing and sealing off the openings 27, 28 so as to cover the ball screw 3 to thereby achieve a function of holding dust generated from the actuator inside the sectioned compartment.
The movable stage 4 is provided with a nut block 41 to which a ball screw nut screwed with the ball screw 3 is formed, a lower plate 42 fixed to the upper surface of the nut block 41, an intermediate plate 43 fixed to the upper surface of the lower plate 42, and an upper plate 44 fixed to the upper surface of the intermediate plate 43. Both side surfaces of the nut block 41 are supported to be slidable in the axial direction of the ball screw 3 by a linear guide rail 31 mounted inside the housing member 2.
The movable stage 4 has a structure in which the upper plate 44 is positioned on the outer side of the hosing member 2, and the intermediate plate 43, the lower plate 42 and the nut block 41 are positioned inside the housing member 2. That is, the upper plate 44 projects outward from the openings 27 and 28, and when the upper plate 44 is connected to an object to be guided, a moving force is applied to the object to be guided.
In addition, rollers 61 to 66 protruded horizontally from the lateral (right and left) side surfaces positioned inside the housing member 2 in the movable stage 4 are provided as bypass means for bypassing the dust-proof belts 29 and 30 in a state of being rotatable. These rollers 61 to 66 are arranged in a manner such that the centrally arranged rollers 63 and 64 are positioned lower than the rollers 61, 62, 65 and 66 disposed both the end sides in the axial direction (further, it is to be noted that although the roller 65 is arranged at a position opposing to the roller 66, the roller 65 does not appear on FIG. 10, and hence, the roller 65 will be described hereinafter as roller (65)).
The respective dust-proof belts 29 and 30 are stretched over the respective rollers 61 to 66 so as to prevent interference of the upper plate 44 projecting outward from the openings 27 and 28 with the dust-proof belts 29 and 30. That is, the dust-proof belts 29 and 30 are stretched over the respective rollers 61 to 66 so as to bypass below the projected portion of the upper plate 44, and more specifically, the left side (upper side on the drawing paper in FIG. 10(a)) dust-proof belt 29 passes above the front side roller 61, is stretched around the lower side of the central roller 63, and then passes above the rear side roller (65). In the like manner as to the right side (lower side on the drawing paper in FIG. 10(a)) dust-proof belt 30 passes above the front side roller 62, is stretched around the lower side of the central roller 63 and then passes above the rear side roller 66.
Since the linear actuator 1 provided with the dust-proof mechanism according to the conventional art has such structure as mentioned above, the openings 27 and 28 formed along the movement locus of the movable stage 4, can always maintain the closed and sealed state by the dust-proof belt 29 and 30. Accordingly, dust generated at or from the sliding portion between the ball screw 3 and the ball screw nut provided for the nut block 41 and the sliding portion between the nut block 41 and the linear guide rail 31 can be prevented from leaking outward through the openings 27 and 28 formed to the housing member 2.
Furthermore, in the linear actuator 1 provided with the dust-proof mechanism according to the conventional art, the dust-proof belts 29 and 30 are arranged inside the housing member 2 so as to be capable of bypassing or detouring below the movable stage 4 which moves along the openings 27 and 28, and accordingly, when the movable stage 4 moves, the closed and sealed state of the openings 27 and 28 by the dust-proof belts 29 and 30 can be always maintained.